add check for config and config.default (opennextjs#464)

* Add check for config.default being undefined

* Add check for both config and config.default

* Create eighty-masks-cheat.md

---------

Co-authored-by: conico974 <[email protected]>

Author: sommeeeer

.changeset/eighty-masks-cheat.md

@@ -0,0 +1,5 @@
+---
+"open-next": patch
+---
+
+add check for config and config.default

docs/pages/config.mdx

@@ -7,10 +7,18 @@ There is two build arguments that you can pass to the `open-next build` command:
 
 ### Configuration File
 
-For personalisation you need to create a file `open-next.config.ts` at the same place as your `next.config.js`, and export a default object that satisfies the `OpenNextConfig` interface.
+For personalisation you need to create a file `open-next.config.ts` at the same place as your `next.config.js`, and export a default object that satisfies the `OpenNextConfig` interface. It is possible to not have an `open-next.config.ts` file, the default configuration will then be applied automatically.
 
 This file needs to be placed at the same level as your `next.config.js` file.
 
+If you have an `open-next.config.ts` file, make sure you have atleast this:
+
+```ts
+export default {
+  default: {},
+};
+```
+
 If you want to take a look at some simple configuration examples, you can check the [simple example](/config/simple_example).
 
 For more advanced use cases, you can check [how to implement custom overrides](/config/custom_overrides).

packages/open-next/src/build.ts

@@ -58,6 +58,12 @@ export async function build(
   // On Windows, we need to use file:// protocol to load the config file using import()
   if (process.platform === "win32") configPath = `file://${configPath}`;
   config = (await import(configPath)).default as OpenNextConfig;
+  if (!config || !config.default) {
+    logger.error(
+      `config.default cannot be empty, it should be at least {}, see more info here: https://open-next.js.org/config#configuration-file`,
+    );
+    process.exit(1);
+  }
   validateConfig(config);
 
   compileOpenNextConfigEdge(tempDir, config, openNextConfigPath);